383
FXUS66 KMFR 281737
AFDMFR

Area Forecast Discussion
National Weather Service Medford OR
1037 AM PDT Sat Jun 28 2025

.Updated AVIATION & MARINE Discussions...

&&

.AVIATION...28/18Z TAFs...Skies are clear across southern Oregon and
northern California this morning and VFR conditions are expected
across the region through this evening. Northerly winds increase
along the coast today with gusts to 30 kt possible at North Bend. It
won`t be as breezy over inland areas, but could still gust to 20 kt
this afternoon and evening. Marine layer stratus is likely to make a
return to the coast north of Cape Blanco tonight, but with a thermal
trough pattern in place, stratus should erode fairly Sunday morning
(~15z). The inland extent of marine stratus will be considerably
less compared to recent mornings as well. So VFR conditions are
expected through the TAF period for inland location. /BR-y

&&

.MARINE...Updated 200 AM PDT Saturday, June 28, 2025...The
thermal trough is strengthening today with increasing north winds.
Small craft conditions will continue in most of the southern
waters through this afternoon. Winds will be strongest south of
Gold Beach.

Moderate to strong winds are likely today, strongest south of Port
Orford where Gales and very steep wind driven seas are likely by
late Saturday afternoon. Meanwhile, Small Craft conditions will
expand over the rest of the waters. These conditions are likely to
last into the start of next week, possibly longer. -
Petrucelli/Hermansen

&&

.PREV DISCUSSION... /Issued 359 AM PDT Sat Jun 28 2025/

DISCUSSION...Currently marine stratus is across Coos County
early this morning. Offshore winds will bring a smaller chance for
Roseburg and areas of the Umpqua Basin to see the stratus reach
this morning. Other than the regular cold spots east of the
Cascades, looking at 40s and 50s for morning temperatures today.

The start of a ridge comes our way later today, and this alongside a
thermal trough along the coast will bring a warm up in temperatures
with more 80s in valleys, although low 90s are forecast in the Rogue
Valley.Sunday is looking to be the warmest of the week for areas
west of the Cascades with a slight increase Monday east of the
Cascades. The probability for Medford to see 100 degrees Sunday is
40-60%, and with clear skies forecast, heading towards the higher
probability to see that. Although there will be a slight cooldown
into early next week, temperatures will still overall be 5 to 15
degrees above normal.

One change that was made in the forecast was to add thunderstorm
potential (15-20%) in portions of Lake and Modoc counties. CAPE
values will still be elevated as they have been in previous
afternoons. Please see the long term discussion to hear more about
the thunderstorm potential that starts Monday. -Hermansen

LONG TERM...As is typical with periods of heat in the region, it
will come to an end with the threat of thunderstorms. With the
ridge passing just to our east and strengthening as it moves over
the Rockies, a trough develops off the coast of California, which
then attempts to move onshore around Monday or Tuesday, taking on
a negative tilt as it does so. This is a classic pattern for
convection here, with the trough tapping into monsoonal moisture
from the south, and taking advantage of the warm surface
temperatures and cooler temperatures aloft to produce instability
across the inland portions of the forecast area.

Not much has changed in regards to the thunderstorm forecast.
Convection may begin as early as Sunday afternoon over far
southern portions of Siskiyou and Modoc counties, depending on how
far north the moisture will get by the peak heating hours of the
afternoon. Confidence on thunder Sunday afternoon is very low, and
wording has been left out of the forecast, but a non-zero chance
is there. Most likely, Sunday will be the "priming-of-the- pump"
day, with little to no convection but definite signs of increasing
moisture. As moisture continues to push north into our area, and
with some support from weak energy aloft, more widespread
convection could then begin as soon as early Monday morning (low
probability), although the most likely scenario has convective
initiation beginning Monday afternoon. I suspect that the area
will be greeted by altocumulus clouds and a feeling of "high"
humidity Monday morning, showing the arrival of the moisture and
potential instability of that afternoon.

Given the pattern, thunderstorms could form up anywhere east of
the coastal ranges Monday (although some models show showers and
stray thunder right along the southern coast Monday), with the
marine layer limiting development along the coast and perhaps into
the Umpqua Basin as well. Most convection should be concentrated
along the Klamath, Siskiyou, and Cascade mountains, as well as the
East Side, with cells then drifting off the terrain and into the
valleys. Steering flow appears weak, so storms may be slow moving,
leading to more hit- or-miss "popcorn" style convection.

Some models then continue shower and perhaps thunderstorm
activity overnight, although confidence on that is low. There is
much more confidence on thunderstorms reforming Tuesday afternoon,
although with the eastward progression of the trough, the best
dynamics and support would then be over northern California and
along and east of the Cascades. Other than location, storm
behavior and character should be very similar to Monday. Storms
could then continue on the East Side into Tuesday night, with
some models even keeping some form of convective showers over Lake
County into Wednesday afternoon.

In short, it is nearly a certain thing that there will be
lighting across the majority of the forecast area both Monday and
Tuesday afternoons. Based on current guidance, we do not expect
very strong or severe thunderstorms, but small hail and gusty
winds are possible. Also, given the high moisture content in the
atmosphere that the models are depicting, these storms will be
wet, and could produce periods of moderate to heavy rainfall. As
always with thunderstorms, lightning will be a threat, not only in
regards to new wildfire starts, but also to anyone attempting to
enjoy outdoor recreation in the area.

One caveat to this scenario will be cloud cover. With this much
moisture entering the area, and with the widespread convection
expected Monday, there may be extensive cloud cover over the area
Tuesday limiting incoming solar energy, keeping temperatures
lower, and limiting instability. This has occured with events
like this in the past, and has significantly reduced thunderstorm
development and blown the forecast on the second or third day,
and this may be another example. Keep up to date with the latest
forecasts as the details regarding this thunderstorm threat become
more clear over the next few days.

Broad cyclonic flow and lower heights then continue over the
area for the remainder of the forecast term (midweek next week).
This should keep temperatures at or just above normal, with
mostly dry conditions, although a few models are showing the
arrival of another trough late in the week, keeping showers and
thunderstorms in mind as we head into next weekend. -BPN

FIRE WEATHER...Updated 300 PM PDT Friday, June 27, 2025...Mostly
low impact fire weather conditions are expected the rest of this
week with fairly typical diurnal (afternoon/evening) breezes,
seasonable humidity and near to above normal warmth.

A strengthening upper ridge will bring hotter weather to all but the
immediate coast this weekend with continued drying. The exception
will be the south coast where afternoon temperatures could get into
the low 80s due to an offshore flow and Chetco effect due to
offshore flow with the thermal trough positioned just off the south
Oregon coast. The thermal trough will also bring enhanced E-NE winds
at the mid slope/ridge level tonight and again Saturday night.
However, overnight recoveries tonight morning not don`t look all
that bad. Saturday overnight recoveries will be moderate, but
probably not enough to be concerned about any watches/warnings.
Temperatures increase across the interior Saturday with widespread
highs in the 90s on Sunday.

Sunday will be the hottest day, with afternoon temperatures near or
at triple digit values for the interior westside valleys.

At the same time, an upper low will form off the California coast
Sunday. At the same time, the upper ridge shifts to the Four Corners
region. This will usher in a south to southeast flow aloft from
California into southern Oregon, and will begin to tap into some
monsoonal moisture that will slide up into northern California
Sunday afternoon and evening. The most likely scenario Sunday
afternoon into Sunday night will be building cumulus over the
mountains in northern California, because there is little or no
trigger, mid level moisture is lacking and instability is marginal
at best. Worst case scenario will be a couple of isolated storms
near the Trinity Horn and points northeastward towards the Shasta
Valley late in the afternoon and early evening hours Sunday. In
summary, Sunday will be the day in which the pump is primed for
whats expected for Monday.

Monsoonal moisture will increase late Sunday night through Monday
and at the same time mid level moisture and trigger will increase.
This will set the table for resulting in thunderstorms over most of
the area inland away from the coast, with storms developing as early
as Monday morning. However, the most likely scenario is convective
showers for Monday morning. Monday afternoon and evening will be the
time period of concern with the shear number and areas affected by
thunderstorms. Steering winds Monday are expected to be light,
therefore storms that develop will be slow movers and could produce
locally heavy rain, but this is still a few days out, so the details
could change.

It`s worth noting the risk for nocturnal storms are next to, but not
zero Sunday night, with an elevated risk for lightning Monday and
Tuesday night. The main storm threat shifts to the Cascades and
points south and east Tuesday into Wednesday. As fuels continue to
dry out and the calendar shifts from June to July, fire danger will
increase. So, be on the lookout for potential Fire Weather
Watches/Red Flag Warnings as we head into next week. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...CA...None.

PACIFIC COASTAL WATERS...Small Craft Advisory until 5 PM PDT Monday
     for PZZ350-356-370-376.

Gale Warning from 5 PM this afternoon to 5 PM PDT Monday for
     PZZ356-376.

&&

$$